In shaping and smoothing the workpiece shape, in order to shorten machining time, to maintain the tightest position tolerance, and to simplify programming the workpiece shape is produced in one cut. To this end in the outward copying of plane workpiece shoulders there are problems with respect to controlling the chip, which problems are particularly troublesome in automatic operations.
German 2,550,333 describes a cutting insert for copy turning which has in addition to the main cutting edge an additional cutting part which extends generally perpendicular to the main cutting edge and away from the main cutting edge. This cutting part can be shaped like a convex circular arc. The disadvantage is that the blade is very difficult to control both during longitudinal as well as inward copying as well as with flat-shoulder turning in contact with the workpiece, in that the differences produced during material removal in the chip thickness make a desired chip monitoring and blade control difficult or impossible.
European 0,133,168 describes a cutting insert for cylindrical turning, inward turning, and transverse turning purposes which had cutting corners that run together at a cutting corner angle .ltoreq.90.degree., which during cylindrical turning and inward turning cuts into the workpiece. Along the cutting edges there is provided in addition a projecting cutting part that should serve as transverse cutter for removing coarse and short chips during the verse turning. The projecting part preceding the acute-angle cutting corner, simultaneously cuts chips from the workpiece. The preceding part of the cutting edge can be convexly curved and lie between two cutting corners or adjacent an obtuse-angle cutting corner. The disadvantage of these cutting inserts is that they cannot be clamped in a standardized holder (according to DIN or ISO standards). In addition the main cutting edge adjacent the acute-angle cutting corner is engaged during longitudinal and inward copying as well as during flat-shoulder turning so that the resulting differences in the chip thickness cannot be controlled or can only be badly controlled with respect to chip formation and cutting stability. In addition in roughing and smoothing of the plane workpiece shoulder there are considerable machining forces which vary considerably so that the turned workpiece surface does not meet tolerances and/or cannot be maintained smooth. With the forces that occur there is also the danger of overloading the cutting insert that can under some circumstances lead to breakage.
Japanese 52-101786 describes a basically triangular or four-cornered cutting insert whose cutting edges each have on one side of a cutting corner a projecting nose-like cutting-edge region whose overall envelope is congruent to the basic shape but is a flatter larger triangle or rectangle. In the region of the nose-like projection there are recesses along the cutting edges. This cutting insert because of its construction can only be used for machining in one direction, that is only for left- or right-hand turning operations since for each cutting corner only one of the adjacent cutting edges is usable. In addition the projecting regions prevent clamping of the cutting insert in the holder.
EP 0,162,029 describes a cutting insert for cylindrical turning, inward copy turning, grinding relief turning, and outward copy turning having cutting corners whose widths are extended and which are formed of a plurality of curved segments which are generally mirror symmetrical to the cutting-corner bisectors. The curvature of the blade arranged furthest from the middle of the cutting insert consists of a circle segment with a radius that is smaller than the radius of the adjacent cutting-edge segment. Even this cutting insert cannot be clamped in a standard cutting-insert holder because of the outwardly projecting cutting corners. The cutting corners are during longitudinal and inward copying as well as flat-shoulder turning in engagement so that as in the above-described cutting inserts there are different in the chip thicknesses which prevent adequate control of the chip and cutting stability.